actix-website/examples/extractors/src/json_two.rs

// <json-two>
use actix_web::{error, web, App, FromRequest, HttpResponse, HttpServer, Responder};
use serde::Deserialize;

#[derive(Deserialize)]
struct Info {
    username: String,
}

/// deserialize `Info` from request's body, max payload size is 4kb
fn index(info: web::Json<Info>) -> impl Responder {
    format!("Welcome {}!", info.username)
}

pub fn main() {
    HttpServer::new(|| {
        App::new().service(
            web::resource("/")
                .data(
                    // change json extractor configuration
                    web::Json::<Info>::configure(|cfg| {
                        cfg.limit(4096).error_handler(|err, _req| {
                            // <- create custom error response
                            error::InternalError::from_response(
                                err,
                                HttpResponse::Conflict().finish(),
                            )
                            .into()
                        })
                    }),
                )
                .route(web::post().to(index)),
        )
    })
    .bind("127.0.0.1:8088")
    .unwrap()
    .run()
    .unwrap();
}
// </json-two>